Requested Authentication Method is not supported on the STS

Question

Our Java app is federated with customers ADFS 3.0 server. There is an issue after sending authentication requests (SP initiated) to ADFS server over SAMLP. It is for intranet use case, where windows authentication was specified on ADFS server in authentication policy. SP app is using ForgeRock's Fedlet library that is forcibly sending RequestedAuthnContext attribute withing SAML authentication request :

samlp:RequestedAuthnContext xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
                             Comparison="exact"
                             >
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:Password</saml:AuthnContextClassRef>
</samlp:RequestedAuthnContext>

We had initially also issue with extranet authentication, where Forms authentication was selected on ADFS. We have solved that with adding Claim custom rule for our RP :

exists([Type == "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/nameidentifier"]) => issue(Type = "http://schemas.microsoft.com/ws/2008/06/identity/claims/authenticationmethod", Value = "urn:oasis:names:tc:SAML:2.0:ac:classes:Password");

Now we are stacked down with intranet use case. On ADFS side we got following error :

MSIS7102: Requested Authentication Method is not supported on the STS.
   at Microsoft.IdentityServer.Web.Authentication.GlobalAuthenticationPolicyEvaluator.EvaluatePolicy(IList`1 mappedRequestedAuthMethods, AccessLocation location, ProtocolContext context, HashSet`1 authMethodsInToken, Boolean& validAuthMethodsInToken)
   at Microsoft.IdentityServer.Web.Authentication.AuthenticationPolicyEvaluator.RetrieveFirstStageAuthenticationDomain(Boolean& validAuthMethodsInToken)
   at Microsoft.IdentityServer.Web.Authentication.AuthenticationPolicyEvaluator.EvaluatePolicy(Boolean& isLastStage, AuthenticationStage& currentStage, Boolean& strongAuthRequried)
   at Microsoft.IdentityServer.Web.PassiveProtocolListener.GetAuthMethodsFromAuthPolicyRules(PassiveProtocolHandler protocolHandler, ProtocolContext protocolContext)
   at Microsoft.IdentityServer.Web.PassiveProtocolListener.GetAuthenticationMethods(PassiveProtocolHandler protocolHandler, ProtocolContext protocolContext)
   at Microsoft.IdentityServer.Web.PassiveProtocolListener.OnGetContext(WrappedHttpListenerContext context)

Could I add/do something for it ? Is it possible to say in custom rules IF IT IS INTRANET, AUTH METHOD IS WINDOWS or something like that?

Answer 1

We have solved this by sending more authentication options and specifying Comparison to minimum

<samlp:RequestedAuthnContext xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
                             Comparison="minimum"
                             >
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:unspecified</saml:AuthnContextClassRef>
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:Password</saml:AuthnContextClassRef>
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml:AuthnContextClassRef>
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:Kerberos</saml:AuthnContextClassRef>
    <saml:AuthnContextClassRef xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">urn:federation:authentication:windows</saml:AuthnContextClassRef>
</samlp:RequestedAuthnContext>

Answer 2

You could always try authnContextClassRef="urn:oasis:names:tc:SAML:2.0:ac:classes:unspecified", which should let the IdP choose whatever it can use. As the SP, you don't really know (and should you care?) which methods are available to the IdP...